From the prior art, numerous methods of detecting traffic violations are known, which methods provide that, upon detection of a certain event, a camera is triggered so as to capture image data of the violating vehicle.
Such events include, e.g., the detection of a vehicle that is exceeding the speed limit or of a vehicle that does not maintain the prescribed minimum distance relative to a reference point or of a vehicle that drives into a prohibited area which is controlled by a traffic light, or the detection of prescribed features of a vehicle, such as exceeding a minimum length.
Depending on the event, the camera can be triggered at least one more time, typically after a predetermined time has lapsed, in order to obtain at least two sets of image data of the violating vehicle.
As to the method according to the present invention, it is immaterial how the camera is triggered. For simplicity's sake, the term triggering will hereinafter be used to cover all possibilities of activating a camera as a result of the detection of a violating vehicle.
As far as the use is concerned, the methods of detecting traffic violations and systems suitable for this purpose can be divided into those in which the measuring range of a measuring system and the object field of a camera are limited to one vehicle lane only, and those in which the measuring range and the object field extend across a plurality of lanes.
Using a measuring system, which can include sensors located on or in the vehicle lane, radar measuring systems, laser measuring systems or video cameras with image processing systems, the vehicles passing through the measuring range or the measuring ranges are measured. Based on the results measured, the vehicle data of interest are determined.
As a rule, these data of interest are the speed of the vehicle, a detection signal and/or the distance from the measuring system. In measuring systems the measuring range of which extends across a plurality of vehicle lanes, the angle relative to the receiver axis of the measuring system might be included among the vehicle data of interest so as to be able to differentiate between vehicles that are in the measuring range or the measuring ranges at the same time and that drive in different vehicle lanes.
Based on the measured results obtained from a plurality of individual measurements that provide a set of measured data, it is possible to extrapolate additional specific vehicle data, such as the travel path of the vehicle through the measuring range or the length of the vehicle. The vehicle-specific data obtained from the measured results of a plurality of individual measurements in combination with identification data, such as date, time of day, location and device identity, are stored in the form of a measured data packet, which means that all sets of measured data being stored for one vehicle are combined to form a measured data packet.
The sets of image data captured by the camera are also stored, and all sets of image data that are linked to a specific vehicle form an image data packet.
According to the state of the art, the measured data packet and the image data packet are stored so as to be uniquely linked to each other. The unique linkage is possible since measuring a vehicle and capturing the image of the vehicle are linked actions that begin in known chronological correlation with respect to each other.
To record a speeding violation, a first image can be triggered, e.g., at the moment at which the measuring device verifies the excess speed, or the photo can be triggered when the vehicle is located at a predetermined distance from the camera, which distance is determined by the speed and a delay in time. In both cases, triggering the camera is initiated by a signal of the measuring device during the measuring procedure, which uniquely links the measured data packets and the image data packets to each other.
Similarly, there are methods in which the camera is triggered by a signal that is independent of the measuring system, e.g., by an induction loop. In this case, the measured data packet is uniquely linked to the associated image data packet by way of the fixed temporal correlation of the acquisition of the data. Thus, if acquisition of the measured data and the image data begins as the vehicle drives over the induction loop, the same time of day is linked to the measured data packet and to the image data packet, thus ensuring that this time of day uniquely links the measured data packet and the image data packet to each other.
According to the state of the art, linking the measured data packets to the image data packets, regardless of how this linkage is implemented, is always implemented by one-to-one and onto mapping, which is based on a known temporal correlation between the data packets. A fixed temporal correlation exists if a first measuring time point and a first image-taking time point temporally coincide or are at a defined temporal distance from each other.
Although the temporal correlation is not fixed, this correlation is known if a time delay is extrapolated from the measured speed and the known or measured distance in order to subsequently trigger the picture when the vehicle is at a predetermined distance from the camera.
One-to-one and onto mapping means that precisely one image data packet is linked to each measured data packet and precisely one measured data packet is linked to each image data packet.
It is immaterial at which moment a measured data packet and an image data packet are linked to each other, i.e., the packets can also be assembled immediately after the data have been acquired and can be jointly stored as a vehicle data packet.
This type of data processing has been found to have drawbacks, especially for solutions in which a plurality of vehicles can be measured at the same time or nearly at the same time.
After the camera has been triggered by a first vehicle, the camera, for a certain length of time, is not ready to be triggered by a second vehicle. How long this time is depends primarily on how many consecutive images are taken each time after a first image has been captured.
In the case of an alleged red light violation, typically after a first picture that captures the vehicle on the stop line, a second and possibly even a third picture follow that show the vehicle even with the traffic light or in the intersection. These pictures taken subsequently are captured either after a fixed time interval has elapsed or as a function of the speed of the violating vehicle at the moment when the violating vehicle is anticipated to arrive at a specific location.
Of vehicles measured within the resultant delay period and identified, by way of the measured results, as violating vehicles, no pictures are captured, which in turn means that there is also no image data packet. For these violating vehicles, it is not possible to generate a vehicle data packet, which means that these traffic violations cannot be documented and therefore no action can be taken against the violators.
A trivial solution to this problem would be to install one camera for each vehicle lane and for this camera to be activated every time a violation is detected that is linked to this particular vehicle lane. However, this entails higher acquisition, installation and maintenance cost for the operator.